Synthesis of azo compounds by rearrangement of hydrazones



United States Patent Ofitice 3,350,385 SYNTHESIS OF AZO COMPOUNDS BYREARRANGEMENT OF HYDRAZONES Leonard Spialter, 2536 England Ave., Dayton,Ohio 45406, and Gerald L. Untereiner, 199 Westhaven Drive, Ottawa 3,Ontario, Canada No Drawing. Filed Aug. 25, 1964, Ser. No. 392,376 2Claims. (Cl. 260-192) ABSTRACT OF THE DISCLOSURE Is-omerized azocompounds are synthesized from hydrazones by molecular rearrangementwith The invention described herein may be manufactured and used formulawherein R R and R are selected from the general class pounds of thegeneral form 3,356,385 Patented Oct. 31, 1367 The method used tosynthesize azo compounds is illustrated by the procedure of reacting atthe temperature of 0 C., methylhydrazine by its dropwise addition to acarbonyl compound, such for example, as propionaldehyde to form thecorresponding hydrazone, which on standing,

band at about 370 millimicrons when they are present, indicate thepossibility of self-catalysed isomerization from the hydrazone (NN=) tothe correazoalkane (N=N). It has been established fied chemically andphysically.

confirmed synthesis of azo compounds from illustrative alkyl hydrazones,have the general formula R,,'N=NR wherein R is methyl and R is n-propyl,isopropyl, n-butyl, s-butyl, and isobutyl. In each the hydrazone isprepared from methyl hydrazone 0 CHaNE[-NH2 Ra Rb 1ret"yl aide yiehydrazi 8 or ketone In the reaction R and organic alkyl group.

However, the hydrazones usable in the practice of this invention areneither limited to those prepared by this R are each hydrogen or anrearrangement:

alkyl hydrazone 4% azo compound The existence of the hydrazone-azo pairconstitutes an example of tautomerism or the coexistence of two orExample I In the illustrative preparation of l-propane azomethane of thecomposition CH -CH CH :N-CH

freshly distilled hydrazone of the boiling point 124 C. is preparedunder an atmosphere of dry nitrogen by reactingdmethylhydrazine CH-NH-NH with propionaldeby e CHsCHzYIZH at C. to produceN-methyl-N'-n-propylidene hydrazine as:

Potassium hydroxide is azeotropically dried with toluene and is crushedto a powder of a desired fineness.

Twenty grams of the freshly distilled N-methyl-N-npropylidene hydrazineof boiling point 124 C., are added to 6 grams of the potassium hydroxidein a one-neck 50 milliliter flask. The flask is fitted with a 10centimeter long fractionating column that is packed with glass helices,and that is provided with a variable take-off distillation head.

Suflicient heat is applied to the flask, from a suitable source, such asfrom an electrical heating mantle or the like, to cause the contents ofthe flask to maintain a refluxing temperature of about 60 C. underordinary laboratory conditions. When the refluxing temperature becomessteady at 60 C., the azo product is removed by means of a stop cock inthe distillation head.

The collection of the distillate is continued until a rise of twodegrees in the temperature is noted, at which time the refluxing iscontinued. The process is repeated until the reaction is completed withno more hydrazine in the distillation flask. The process requires about2 hours.

The refractionation of the collected distillate illustratively yieldsabout 65 percent of l-propaneazomethane of a boiling point 58.5-59.5 C.at 736 mm. Hg and of the physical properties 11 1.3856 and 11 0.7485 andof the composition The same method of preparation of hydrazones isfollowed in the synthesis of the alkyl hydrazones, with the exception ofN-methyl-N-isopropylidene hydrazine. This synthesis differs from thesynthesis of the remaining hydrazones only in that ethanol is used assolvent, whereas no solvent is used for the synthesis of the remainingfour hydrazones that are listed herein. There is no material differencein the ease of preparation, so the use of the solvent is believed to beof little significance.

Additional typical illustrative reactions appear in Table I and Table IIhereinafter.

4 The hydrazones prepared by the reaction at 0 C. of methyl-hydrazinewith acetone 6 OH3-C-CH; to yield N-methyl-N-isopropylidene hydrazine ofthe composition CH NHN=C(CH n-butyraldehyde 0 ti CHaCHzCHz H to yieldN-methyl-N'-n-butylidene hydrazine of the composition CH NHN=CHCH CH CHmethylethylketone or Z-butanone CH COC H to yield N-rnethyl-N'-S-butylidene hydrazine; and with isobutyraldehyde O (CI-IshCH H to yieldN-methyl-N'-isobutylidene hydrazine of the composition CH NH-N=CHCH(CHetc., respectively, were isomerized to their respective azo compounds.For each synthesis approximately 20 g. of the hydrazone was added to 6g. of dried potassium hydroxide (KOH) pellets contained in a ml. flask.The flask was fitted with a 10 cm. glass-helices packed column and asmall distillation head. Sufficient heat was applied with an electricGlas-Col heating mantle to cause refluxing. When the temperature becamesteady, the product was removed by means of a stopcock on the distillinghead. Collection was continued until a two degree rise in temperaturewas noted, at Which time refluxing was continued. The above process wasrepeated until the reaction was complete, i.e., no more hydrazoneremained in the distilling flask.

A true boiling point for each product was established by redistillationthrough a 5 cm. column. To complete the identification of each compound,the density at 25 C. an 0 C., refractive index at 25 C., infraredabsorption spectrum, molecular refractivity (calculated and observed),and elemental analysis were obtained.

The preparative data are summarized in Table 1, characteristic physicalproperties appear in Table II.

In Table I the N-methyl-N-n-propylidene hydrazine was isomerized tol-propaneazo-methane, or

was rearranged to CH N=NCH(CH The N-methyl- N'-isopropylidene hydrazinewas isomerized to 2-propaneazomethane, or CH NHN=C(CH was rearranged toCH N=N-CH(CH The N-methyl-N'-n butylidene hydrazine was isomerized tol-butaneazomethane, or CH NHN=CHCH CH CH was rearranged to CH N=N(CH CHThe Nmethyl-N-S-butylidene hydrazine was isomerized toZ-butaneazomethane, or CH NHN :0 (CH CH CH was rearranged to CH N :NCH(CH CH CH The N-methyl-N-isobutylidene hydrazine was isomerized toI-(Z-methylpropane) azomethane, or

was rearranged to CH N=NCHC(CH YIELDS OF UNSYMMETRICAL ALKYL AZOALKANESFROM REARRANGEMENT OF HYDRAZONES Starting HydrazoneN-methyl-N-n-pr0pylidene hydrazine Nmethyl-N-isopropylidene hydrazineN-rnethyl-N-n-butylidene hydrazine. N-methyl-N-s-butylideue hydrazine.N-methyl-N-isobutylidene hydrazine Z-butaueazomethane Azo Compoundl-propaneazomethane Zpropaneazomethane l-butaneazomcthane1-(2-methylpropane) azomethariezII: CHaN TABLE IL-PHYSIOAL PROPERTIES OFUNSYMMETRICAL ALKYL AZOALKANES Density (g./rnl.) Molecular2gefcractivity at Berlin Pressure g Refractive Compound Point 0.) (mm. Hg)Index (11 25 0. C. Cale. Obs. M

l-propaneazomethane 58. -59. 5 736 1.3856 0. 7485 O. 7782 27. 05 27. 012-propane-azomethane 48. 5-49. 5 744 1. 3782 0. 7327 0. 7605 27. 05 27.11 l-butane-azomethane 89-90 734 1. 3974 0. 7674 0 7917 31. 67 31 46abutane-azomethane:III: 77. 5-78 740 1. 3926 0. 7560 01 7313 31. 67 311so 1-(2-methy1propane)-az0methane 79. 0-79. 5 739 1, 3918 0. 7543 0.7798 31. 67 31. 62 It is to be understood that the synthesis of azocompowdered potassium hydroxide in a flask fitted with 8 pounds that 1sdisclosed herein is illustrative of an experifractionating column packedwith glass helices and promentauyfonfifmed seljies reactions andresults, and 15 vided with a variable take-off distillation head,heating the flask to a refluxing temperature of about 60 C., removingthe l-propaneazomethane product by means of a stop cock in thedlstlllation head collecting the distillate until a rise of two degreesin the temperature is noted at g ;22 :2222 g z ifg g by the rearrangewhich time the refluxing is continued, and repeating the CH -NHN=CR Rwherein R and R are hydrogen or an alkyl group con- References Cltedtaining 1 to 4 carbon atoms consisting of the steps of re- 25 Chattawayet t Chem. (London), VOL f fluxing the hydrazone under a dry nitrogenatmosphere 1930, pp

the final roduct y distillation Gershinowitz et al: J. Chem. Phys., vol.2, pp. 273-282 2 Th f 1 th f (1934) the g g ggg 0 Preparing'propaneazome am 0 3O Ramsperger: J. Am. Chem. Soc., vol. 51, pp.918-921 CHARLES B. PARKER, Primary Examiner. comprising the steps ofreactlng about 20 grams of N- methyl-N-n-propylidene hydrazine with sixgrams of dry F. D. HIGEL, Assistdnt Examiner.

tion defined by the appended claims.

We claim:

1. THE SYNTHESIS OF AN AZO COMPOUND BY THE ARRANGEMENT OF A HYDRAZONE OFTHE FORMULA